Fix heading sizes

Change-Id: Ibbe378d3aba4325f1b5d2e76e2814c2355959df8
diff --git a/inst/reveal.js-4.6.1/dist/theme/ids.css b/inst/reveal.js-4.6.1/dist/theme/ids.css
index 6493e18..d1b4a06 100644
--- a/inst/reveal.js-4.6.1/dist/theme/ids.css
+++ b/inst/reveal.js-4.6.1/dist/theme/ids.css
@@ -30,8 +30,8 @@
   --r-heading1-text-shadow: none;
   --r-heading1-size: 2em;
   --r-heading2-size: 1.35em;
-  --r-heading3-size: 1.1em;
-  --r-heading4-size: 1em;
+  --r-heading3-size: 0.9em;
+  --r-heading4-size: 0.7em;
   --r-code-font: monospace;
   --r-link-color: #2a76dd;
   --r-link-color-dark: #1a53a1;